Patent GB-942661-A (GB)
Title: Improvements in or relating to magnetizing means
Filed: 1960-03-14
Abstract: 942,661. Magnetic data-storage apparatus. BURROUGHS CORPORATION. March 14, 1960 [March 20, 1959], No. 8960/60. Heading H3B. [Also in Division H1] In a non-destructive read-out arrangement for a thin magnetic film of the order of 2000 Angstrom units thick, the cross-section of a read conductor in proximity to the surface area of the film is reduced over a portion of the film so that the magnetizing field produced by a read current is more intense in this portion than in the remainder of the film. In this manner a limited switching of the film magnetization takes place, the switching being restricted to the portion subjected to the higher magnetizing current. When the read current terminates, the switched portion is restored to its original state by the magnetization preserved in the remainder of the film. As shown, an information storage matrix comprises thin films 211-214 of nickel-iron alloy adjacent to which is provided read conductors 231, 232, write conductors 271, 272 and information conductors 281, 282, all formed of brass shim material and insulated from one another. In addition, a copper sense wire is provided. The read conductors are provided with notches as shown over a portion of each film to effect the non-destructive read-out operation. These conductors may alternatively be formed from folded tapes or from braided or parallelarranged fine wires having constricted portions, Fig. 4 (not shown). Operation of the apparatus is controlled by a control signal source 100, the films being initially polarized in the easy direction of magnetization which lies parallel to the read and write conductors 231, 271 and 232, 272. To record information in a selected column, a write current source 101 is energized, and current in a write conductor 271 or 272 rotates the polarization of films 211, 213 or 212, 214 to the hard direction of magnetization which lies parallel to the information conductors 281, 282. The information current source is then energized and positive or negative currents are passed through the information conductors according to the information received. These currents, in combination with the write current, cause a partial polarization rotation. The write current is terminated before the information current, and each film becomes polarized along the easy axis in a direction determined by the magnetic conditions obtained after partial rotation has been effected. Non- destructive read-out is caused by current in a notched read conductor 231 or 232 which is selectively applied by a read-current source and effects a localized rotation of polarization direction to the hard direction. As a result, pulse voltages are induced in the sense wires 291, 292 the polarity of which is determined by the directions of movement of the localized magnetizations of the respective films. When the read current terminates, the films restore to their previous magnetic states. The identity of the sense pulses is determined by a data utilization device 104. In a modification, Fig. 3 (not shown), the conductors 231, 232 serve as both read and write conductors and are connected to the write and to the read current sources both of which have high impedances when not operative. In this case the write current is of higher magnitude so as to effectively magnetize the whole area of the films. Specification 937,823 is referred to.